To preview an image while hovering over it, there are two display options: Image Preview and Metadata Preview.

You may catch a larger glimpse of content in list, thumbnail, and masonry grid.  To select where to apply the preview, go to Settings > Configuration Options > Defaults > Tooltip Preview Display On & Tooltip Preview Style. Then, check the boxes of the locations where you want to see the preview and your preview options.

To preview the Image, select "Image" in the Tooltip Preview Style Menu.

Then, simply hover your mouse over the file and an expanded preview will emerge on the side.

For more options, proceed by clicking on the file. 

To preview the file Metadata Information, select the "Information" option under the "Tooltip Preview Style Menu."

The options of Metadata to display include Basic Metadata, File Metadata, and Custom Fields.  To select which to display, check the box next to each option.

Hover your mouse over the file and the Metadata will appear.